1. Field of the Invention
The present invention relates to a method for delivering a fine particle dispersion and a device for delivering a fine particle dispersion by use of a microflow-channel.
2. Description of the Related Art
In recent years, various research has been made into performing chemical reactions, unit operations or the like at a scale in the order of micrometers. In connection with this, methods and devices have been suggested for extraction, separation, mixing or particle-formation, focussing on the short diffusion times.
Dispersions of fine particles having a specific gravity greater than that of the liquid medium thereof and having a size in the order of microns are ordinarily caused to flow in channels (or pipes) having cross-section diameter in the order of centimeters or more.
However, there has not been suggested any method for causing a dispersion of fine particles having a specific gravity greater than the liquid medium thereof and having a size in the order of microns to flow in channels having an inside diameter in the order of micrometers.
This is based on the following reason: when a dispersion of fine particles having a specific gravity greater than the liquid medium thereof and having a size in the order of microns is caused to flow in channels having an inside diameters in the order of micrometers, problems of fine particles sedimentation causing clogging of flow arise since the specific gravity of the fine particles is larger than that of the medium. In particular, a fluid in a channel having an inside diameter in the order of micrometers is known to flow in the state of laminar flow due to the inside diameter being small. But with laminar flow, there is no stirring inside the fluid and accordingly fine particles which sediment while moving with the flow do not receive any upwards force and are thus deposited on the bottom of the channel. For this reason, the problem of the particles sedimenting occurs in a short period of time. When the microflow-channel becomes blocked up, it is very difficult to free the blockage resulting in a more serious problem.
Hitherto, it has been considered that the effect of gravitation on fine particles in a channel having an inside diameter in the order of micrometers becomes relatively small (see, for example, “Kagaku Kogaku (Chemical Engineering)” vol. 66 No. 2 (2002)). However, it has been found that dispersed fine particles in the order of microns sedimenting under gravitation cause problems. This is because condition of the channel relative to the gravitational direction is not ordinarily considered.
In cases where a dispersion of fine particles in the order of microns is caused to flow in a channel having an inside diameter in the order of centimeters or more, rarely are fine particles sedimented so as to be deposited on the bottom of the channel. This can be considered as follows: the sedimentation of the fine particles should theoretically occur; however, since the fluid in the channel flows in a turbulent flow state stirring occurs. This means that practically fine particles do not sediment so no deposition of the particles on the bottom face of the channel occurs.
As the above-mentioned methods for performing chemical reactions, unit operations or the like at a micrometer-scale, for example, a solvent-extracting method using a micro-fluid-system is suggested (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-361002). However, this is not a method for use in a system which contains fine particles.
The following methods are also provided: a method of forming mono-dispersed metal nanometer particles continuously; a method of growing crystal by use of the above nanometer particles as nuclei; and a method of performing desaltion or removal of decomposition products continuously from a colloidal dispersion of nanometer particles. However, the size of the metal nanometer particles is described as 10 nm or less, and particles larger than this size are never referred to (see, for example, JP-A No. 2003-193119).
Also suggested is a new method of using a micro-mixer to produce morphologically uniform micrometer particles and nanometer particles continuously, and the use of this method for encapsulating active substances, and particles produced by this method. However, the size of the produced micrometer particles is from about 1 to about 1000 μm (about 10 μm in the working examples). In cases where a dispersion containing particles having a larger specific gravity than that of the liquid medium thereof are delivered in a microflow-channel, sedimentation or the like occurs within the channel causing the flow to be hindered or the channel to be blocked up (see, for example, Japanese Patent Application National Publication (Laid-Open) No. 2003-500202).
In short, no method for delivering a dispersion of fine particles of the order of microns stably and without blocking up the dispersion-delivering channel has been suggested. A method of synthesizing fine particles and delivering a liquid in a microflow-channel, wherein fine particles are dispersed, for example, has been carried out. However, the size of the fine particles is limited to a size in the order of nanometers. In methods for producing particles, or the like, of the order of microns by use of a microreactor, the particles are discharged from the system immediately after the particles are produced. Thus, no method wherein a liquid containing the particles is delivered in the microflow-channel has been suggested.
As described above, hitherto, no method or device has been suggested which: causes no sedimentation or blocking; is capable of delivering fine particles of the order of microns stably; and also, is capable of performing effective washing.